Fluorescent lamp controlling arrangement

Abstract

A method for controlling the luminescence of a fluorescent lamp in which a light sensor operates in response to light other than that from the fluorescent lamp striking it to increase the luminescence of the lamp.

What is claimed is: 
     
       1. A method of controlling the amount of luminescence provided by a lamp used for backlighting a liquid crystal display including sensing the amount of light incident on said display other than that provided by said lamp and increasing the luminescence provided by said lamp as said incident light increases wherein said luminescence increases from a minimum threshold, which minimum threshold is held constant until said incident light reaches a given minimum. 
     
     
       2. A method of controlling the amount of luminescence provided by a lamp according to claim 1, wherein said luminescence increases from said minimum threshold to a maximum in a predetermined manner as said incident light increases. 
     
     
       3. A method of controlling the amount of luminescence provided by a lamp according to claim 2, wherein said minimum threshold is held constant until said incident light reaches a given minimum. 
     
     
       4. A method of controlling the amount of luminescence provided by a lamp according to claim. 2, wherein said luminescence increases constantly to said maximum as said incident light increases. 
     
     
       5. A method of controlling the amount of luminescence provided by a lamp in accordance with any one of claims 1, 2 or 4 wherein said lamp is a fluorescent lamp. 
     
     
       6. A sensing circuit from a fluorescent lamp connected to a ballast means for said fluorescent lamp which ballast means includes a light control circuit, said sensing circuit including a light sensor which produces a signal representative of incident light impinging upon it, said sensing circuit being operable from power derived from said ballast means and controlling said light control circuit to increase the luminescence of said fluorescent lamp as said incident light increases. 
     
     
       7. A control circuit for a fluorescent lamp connected to a ballast means for said fluorescent lamp, said ballast means having two circuit nodes, said control circuit including a light sensor which produces an output signal representative of light striking it, a first stage amplifier, said light sensor being connected to said first stage amplifier which amplifies the output signal of said light sensor, said first amplifier having an output, a second stage connected to the output of said first stage amplifier, said second stage operating as a current sink and connected to said ballast means to increase the light from said fluorescent lamp as said light striking said light sensor increases, said control circuit being connected to said two circuit nodes of said ballast means and receiving operating power for its entire operating cycle from said circuit nodes. 
     
     
       8. A control circuit for a fluorescent lamp as claimed in claim 7, wherein said first stage amplifier is an NPN transistor. 
     
     
       9. A control circuit for a fluorescent lamp as claimed in claim 8, wherein said second stage current sink is an PNP transistor. 
     
     
       10. A sensing circuit for a fluorescent lamp connected to a ballast means for said fluorescent lamp which ballast means includes a light control circuit, said sensing circuit including a light sensor which produces a signal representative of incident light impinging upon it, said sensing circuit controlling said light control circuit to increase the luminescence of said fluorescent lamp as said incident light increases, wherein said sensing circuit maintains a minimum threshold luminescence until said light sensor signal indicates that a given minimum of incident light is impinging on it. 
     
     
       11. A sensing circuit for a fluorescent lamp according to claim 10, wherein said sensing circuit increases said luminescence from said minimum threshold to a maximum in a predetermined manner as said signal from said light sensor increases with increasing incident light 
     
     
       12. A sensing circuit for a fluorescent lamp according to claim 11, wherein said sensing circuit maintains said minimum threshold luminescence until said light sensor signal indicates that a given minimum of incident light is impinging on it. 
     
     
       13. A sensing circuit for a fluorescent lamp according to claim 11, wherein said sensing circuit increases said luminescence constantly as said signal from said light sensor increases.